Bistable Electrical Switching Using a Crown Ether-Based Monolayer Electrolyte on WSe Field-Effect Transistors with Various Salts.

Bistable electrical switching using a crown-ether-based electrolyte on WSe field-effect transistors (FETs) is measured for four salts: LiClO, NaClO, Ca(ClO), and LiCl. The solid-state monolayer electrolyte comprises cobalt crown ether phthalocyanine in which cations are solvated by 15-crown-5 ethers. The switching mechanism is the toggling of cations through the crown ether cavity in response to an applied field, creating low and high resistance states in the WSe channel. This work shows that bistability is not unique to Li and extends to other perchlorate-based salts with Na and Ca cations. LiClO induces the largest sheet density (2 × 10 cm) followed by Ca(ClO) (1 × 10 cm) and NaClO (0.8 × 10 cm). The impact of the anion was evaluated by replacing LiClO with LiI and LiCl. A homogeneous deposition of LiI could not be achieved, and LiCl only induced 0.2 × 10 cm-an order of magnitude less charge than the perchlorate-based salts. Devices with LiCl required the largest voltages to achieve switching and had the smallest ON/OFF ratio in a 6 h state retention test. The results point to the anion playing a critical role in bistability, and Li as the best performing cation in terms of doping density, minimum switching voltage, and state retention.